. >> woodruff: the renewed concern over mass shootings in the united states-- and how to prevent them-- was highlighted today in events ranging from an anniversary appeal to a colorado court hearing. the day began with solemn remembrance of an attack that left a lawmaker gravely wounded. . bells tolled across tucson, arizona, this morning in ceremonies broadcast on local t.v. the ringing two years to the day after a gunman opened fire at an outdoor political event for then congresswoman gabrielle giffords six people were killed and gabrielle giffords was shot in the head. she later left congress to focus on her recovery. the gunman, jared lee loughner, pleaded guilty and was sentenced to life in prison. now, in the wake of the latest mass shooting in newtown, connecticut, giffords and her husband, mark kelly, have opened a new campaign against gun violence. they appeared today in an interview with diane sawyer of abc news. >> i have a gun. gabby and i are both gun owners. we are strong supporters of the second amendment. but we've got to do something to keep the guns from getting in t